It has been previously proposed to employ an abrasive cutting chain on the guide bar of a motor driven chain saw for cutting rock and other hard material as shown in U.S. Pat. No. 2869534 of Stihl, issued Jan. 20, 1959, and U.S. Pat. No. 2912968 of Stihl, issued Nov. 17, 1959. However, there are many problems when attempting to cut stone, concrete, and masonry or other hard material, with a chain saw using a chain having abrasive cutting elements. The abrasive cutting elements are formed of hard abrasive particles such as diamonds or silicon carbide held in a metal matrix which is attached to the cutting link by welding with sufficient strength to resist the high shock and high heat conditions of abrasive cutting. This requires complicated and expensive cutting links. As a result such cutter elements may be rotatably mounted on the links to reduce wear as in Stihl U.S. Pat. No. 2,912,968.
In addition, the drive sprocket and guide bar used in a chain saw for guiding the movement of the abrasive cutting chain, frequently become coated with rock dust or other comminuted material, which causes wear and friction that may unduly load the chain saw motor. This rock dust accumulation causes abrasion of the guide bar drive track, drive sprocket, and the chain links resulting in rough running and heating of the guide bar and the chain. Such abrasion also results in widening of the guide bar track and wear of the sprocket teeth, which causes the chain to be laterally unstable. In addition, the rock dust or other comminuted material can penetrate between the chain links causing wear of such links and their pivotal pin connections which may result in chain breakage. Also the chain can jump off the guide bar or sprocket due to the accumulation of the rock dust on the guide bar and sprocket. These problems are discussed in U.S. Pat. No. 3,384,417 of Mylewski, issued May 21, 1968. Attempts to overcome these problems have included the use of flow tubes on the chain saw to produce pressure streams of water directed against or through passages in the guide bar in order to clean out the rock dust from the guide bar track and to cool and lubricate the track and the chain moving on such track, as shown in U.S. Pat. No 3,593,700 of McNulty, issued Jul. 20, 1971, and U.S. Pat. No. 4,920,947 of Scott et al., issued May 1, 1990.
Another problem with an abrasive cutting chain saw is the need to regulate the power of such saw when cutting through rock and other material which is of varying consistency and hardness. It has been proposed in U.S. Pat. No. 4,181,115 of Weisner, issued Jan. 1, 1980, to provide a power control which senses reduced power consumption of the saw motor and generates a control signal to increase the speed of the saw feeding the chain through the material being cut or to decrease such speed when excessive power consumption is sensed. However, this does not eliminate the many other problems associated with the use of such a chain saw and its accompanying guide bar, as discussed above.
It has also been proposed more recently in German patent No. 3,332,051 of Mayer, issued Mar. 15, 1984, and in U.S. Pat. No. 4,920,947 of Scott et al. cited above to provide an abrasive cutting chain saw with a saw chain having abrasive cutting elements each secured on a pair of side links on opposite sides of the chain.
Another patent of interest is U.S. Pat. No. 4,461,269 of Elliott, issued Jul. 24, 1984, which is directed to the design of a special abrasive resistant chain saw sprocket having replaceable carbide steel teeth to overcome the abrasion caused by the rock dust produced by the chain saw.
All of these prior saw chains engage a track on a guide bar and are driven by a drive sprocket, unlike the abrasive cutting chain of the present invention, which wear quickly to cause most of the above-mentioned problems. The abrasive cutting apparatus of the present invention eliminates both the guide bar and the usual drive sprocket. In addition, the prior cutting elements extended outwardly of the chain for cutting in a conventional manner, and are not inverted to face inwardly and to engage a motor driven pulley in the manner of the present invention.
As a result of these many problems, the abrasive cutting of rocks, concrete, masonry and the like, is still performed, to a large extent, by abrasive cutting cable or wire employing abrasive cutter elements. In recent years the abrasive cutter elements are in the form of beads mounted in spaced relationship on a flexible cable or wire by shock absorbing coil springs, as shown in U.S. Pat. No. 4,674,474 of Baril, issued Jun. 23, 1987. This process of cutting rocks and other similar material using abrasive wire has been accepted practice in the stone cutting industry for hundreds of years. Even though this conventional stone cutting process has been improved in recent years by the introduction of a flexible cable or wire having abrasive cutter elements such as diamond matrix beads resiliently mounted on such cable or wire as shown in the above-cited Baril patent, there remain a number of problems associated with this cutting process. First, the abrasive cutting cable or wire must be made into a plurality of different lengths to match specific cutting applications including the size and location of the rock, concrete or other material being cut. In addition the cutting machine driving the flexible cable must be provided on a track of sufficient length of travel to allow such machine to pull the selected length of cutting wire through the rock to complete the cut. Second, cable breakage occurs frequently and is extremely difficult to repair in the field resulting in the loss of expensive diamond cutting elements and interruption in operation of the cutting equipment for significant periods of time for repair or until replacement cables can be supplied. Third, diamond cutting beads mounted on the cable find a preferred rotational location on the cable and wear through for premature breakage of the diamond beads with up to thirty-five percent of the diamond wear life remaining. Fourth, breakage of a cutting cable is extremely dangerous when it occurs in the field since it can strike the operator or other persons in the work area, and this danger also exists when the cable completes a cut due to the sudden release of stored energy in the cable. Such a cutting cable follows a path of decreasing radius as it is pulled through a cut in a rock thereby increasing the probability of breakage as it completes the cut. Also, unlike relatively stiff cables, a chain with pivoted links forms at its looped end an unrestrained parabolic curved cutting path through the rock or other work piece. Cables however have a considerable resistance to bending and develop high stress points when they move along a course which tends to move the cable out of its cutting plane and to cause breakage of the cable.
It has been found that the problems associated with an abrasive cutting cable of conventional construction and those associated with an abrasive cutting chain saw employing a conventional guide bar, can be reduced or eliminated by the present invention in which the abrasive cutting cable is replaced by a flat link abrasive cutting chain which is inverted and operated without using a guide bar. Of course, by eliminating the use of a guide bar and a drive sprocket, the improved abrasive cutting chain system of the present invention eliminates the problems of abrasive wear of the sprocket and the guide bar track and lateral instability of the chain due to such wear. Thus, in the present invention, the chain is inverted so that its cutter links have their abrasive cutting elements facing inward and such cutting elements are engaged by a motor driven pulley in order to drive the cutting chain. In addition, the operation of such inverted cutting chain can be improved by causing an outer projection portion on each of the center links of the chain which extends outwardly therefrom to engage a groove in each of a pair of idler pulleys which guide movement of the chain to provide lateral stability during cutting and apply tension to the chain. Such improved abrasive cutting chain is assembled in standard lengths which are connected together by releasable connector links that may be disconnected and reconnected manually to provide chain assemblies of many different selected lengths. In addition by removing selected standard length or adding standard lengths, the length of the assembled chain can be changed using the releasable connector links to suit different cutting conditions and to replace broken standard lengths in the field.